Add instructions for using sockets establishing db

source/guides/administrator.rst

@@ -31,6 +31,7 @@ Learn how to get Mattermost running on your environment.
    Installing on RHEL 6.6 </install/install-rhel-66.rst>
    Installing on RHEL 7.1 </install/install-rhel-71.rst>
    Installing on CentOS, Oracle Linux, and Scientific Linux </install/install-centos-oracle-scientific.rst>
+   Instructions on setting up a socket-based Mattermost database </install/sockets-db.rst>
    /install/ee-install*
    /install/deploy-bitnami*
    /install/docker-local*

source/install/sockets-db.rst

@@ -0,0 +1,108 @@
+Using Sockets for Database
+====================
+
+Mattermost requires a database back-end. If you plan to run it on the machine,
+install MySQL or PostgreSQL as the database. In this document let's understand how
+you can use sockets for setting up the database.
+
+
+MySQL
+-----
+
+.. code-block:: bash
+
+    $ mysql -u root -p
+    CREATE DATABASE mattermostdb;
+    CREATE USER mmuser IDENTIFIED BY 'mmuser_password';
+    GRANT ALL ON mattermostdb.* TO mmuser;
+
+
+PostgreSQL
+----------
+
+- Install and configure PostgreSQL.
+- Choose between TCP or UNIX Socket, and jump to the corresponding section.
+
+With TCP socket
+---------------
+
+- Create the new user while connecting to the server as ``postgres`` user
+  (you will be prompted for a password for the new user):
+
+   ``sudo -u postgres createuser -P mmuser``
+
+- Create the Mattermost database, owned by ``mmuser`` user:
+
+  ``sudo -u postgres createdb -O mmuser mattermostdb``
+
+- In the connections and authentications section, set the ``listen_address`` list
+  line per your needs:
+
+   .. code-block:: bash
+
+      /var/lib/postgres/data/postgresql.conf
+      listen_address = 'localhost,my_local_ip_address'
+
+  You can use '*' to listen on all available addresses.
+
+- Then add a line like the following to the authentication config:
+
+  .. code-block:: bash
+
+     /var/lib/postgres/data/pg_hba.conf
+     # TYPE  DATABASE        USER            ADDRESS                 METHOD
+     # IPv4 local connections:
+     host    all             all             ip_address/32   md5
+
+- Run the setup using:
+
+  .. code-block:: bash
+
+     $ psql --host=ip_address --dbname=mattermostdb --username=mmuser --password
+
+With Unix socket
+----------------
+
+- Create the new user while connecting to the server as ``postgres`` user:
+
+  .. code-block:: bash
+
+     sudo -u postgres createuser mattermost
+
+- Create the Mattermost database, owned by ``mattermost`` user:
+
+  .. code-block:: bash
+
+     sudo -u postgres createuser mattermost
+
+- Setup the Unix socket by adding the following line to ``/var/lib/postgres/data/pg_hba.conf``:
+
+  .. code-block:: bash
+
+     local    mattermostdb    mattermost    peer
+
+- Restart postgresql.service.
+
+- Run the setup using:
+
+  .. code-block:: bash
+
+     sudo -u mattermost psql --dbname=mattermostdb --username=mattermost
+
+
+Configuring Mattermost
+----------------------
+
+- Mattermost is configured in ``/etc/webapps/mattermost/config.json``.
+  Strings need to be quoted.
+
+- The ``DriverName`` setting: ``mysql`` for MySQL and ``postgres`` for PostgreSQL.
+
+  The ``DataSource``:
+
+  - For MySQL, set it to ``mmuser:mmuser_password@unix(/run/mysqld/mysqld.sock)/mattermostdb?charset=utf8mb4,utf8``.
+  - For PostgreSQL
+    - TCP socket: ``postgres://mmuser:[email protected]:5432/mattermostdb?sslmode=disable&connect_timeout=10``    
+    - Unix socket: ``postgres:///mattermostdb?host=/run/postgresql``, where ``mattermostdb`` is the name of the database and ``/run/postgresql`` is the directory containing the Unix socket.
+
+